They are evergreenshrubs and trees growing to 35 m tall. The foliage consists of slender, much-branched green to grey-green twigs bearing minute scale-leaves in whorls of 5–20. The flowers are produced in small catkin-like inflorescences; the flowers are simple spikes. Most species are dioecious, but a few are monoecious. The fruit is a woody, oval structure superficially resembling a conifer cone made up of numerous carpels each containing a single seed with a small wing.[1][3] The generic name is derived from the Malay word for the cassowary, kasuari, alluding to the similarities between the bird's feathers and the plant's foliage,[4] though the tree is called rhu in current standard Malay.

Commonly known as the she-oak, sheoak, ironwood, or beefwood, casuarinas are commonly grown in tropical and subtropical areas throughout the world. The tree has delicate, slender ultimate branches and leaves that are no more than scales, making the tree look more like a wispy conifer. The plants are very tolerant of windswept locations, and are widely planted as windbreaks, although usually not in agricultural situations.

C. equisetifolia is a common tropical seashore tree known as Common Ironwood, Beefwood, Bull-oak, or Whistling-pine and is often planted as a windbreak. The wood of this tree is used for shingles, fencing, and is said to make excellent, hot burning firewood.

C. oligodon has been planted in New Guinea in an ancient (more than 3,000 years) silviculture by highland gardeners practicing an intensive traditional permaculture. The wood of this tree is used for building-timber, furniture and tools and makes excellent firewood. The tree's root nodules are known to fix nitrogen, and it is traditionally prized for its ability to increase the soil's fertility. Its abundant leaf-fall is high in nitrogen and traditionally prized for mulch.

The resin exuded from some casuarinas is edible and was a food source for Aboriginal people.

Gardeners in Bermuda can appreciate that all parts of the casuarina tree (needles, sawdust, bark, and prepared mulch) can be useful in lowering the soil pH, as Bermuda's topography consists of naturally high pH limestone rock, and perhaps only a foot of red or sandy soil. Lowering soil pH makes the soil more acidic, which can help Bermuda's biodiversity by growing acid-loving plants such as blueberries, blackberries, azaleas, rhododendrons, and such plants that may be seen in similar hardiness zones as Bermuda (USDA 9-11), such as plants found in New Zealand and Florida, which naturally have a lower pH soil than Bermuda, albeit some other environmental differences as well.

C. equisetifolia is widespread in the Hawaiian Islands where it grows both on the seashore in dry, salty, calcareous soils and up in the mountains in high rainfall areas on volcanic soils. It is also an introduced, invasive plant in Bermuda,[12] where it was introduced to replace the Juniperus bermudiana windbreaks killed by juniper blight in the 1940s. Now the ironwoods are growing on cliffs and sandy slopes strangling all surrounding plants, or covering them in needles; they also erode the cliffs by digging their roots deep into them and splitting them apart.

Casuarina and Allocasuarina spp are strongly suspected of having allelopathic properties, as evidenced by the total or near absence of understory once a mat of litter develops around the plants.